As is evident from figure 8, the USPS multi-line with ZIP+4 curve (Alt. B. [low]) has an elbow in it, with no increase in the savings level occurring until ZIP+4 usage exceeds about 20 to 25 percent. USPS defends this “elbow” on the grounds that up to about 20

percent ZIP+4 usage, the read redundancy in the address

advantage

from

the

multi-line

OCR.

[n

other

words,

and the ZIP+4 USPS believes

code negates any that the higher

quality mail will be the first to use ZIP+4, and thus there

from

multi-line

processing.

OTA

was

unable

to

establish

will be no immediate benefit a satisfactory engineering

justification

for

this

redundancy

effect,

and

USPS

was unable to

provide

a detailed

explanation. as multi-line

Therefore, while OTA included the elbow in the USPS-estimated curve used alternative B [low], OTA excluded the elbow for alternatives B [median] and

B [high]. For these multi-line ZIP+4 usage and savings.

alternatives,

OTA

assumed

a

linear

relationship

between

For modeling purposes, OTA converted the figure 8 curves into a set of normalized linear equations using ZIP+4 usage as the independent variable and usage savings factor as the dependent variable. A usage savings factor of 1.0 equates to 100 percent of the savings projected for the single-line OCR alternative at 90 percent ZIP+4 usage. The set of curves corresponding to the linear equations is shown in figure 9. The slope of the single-line OCR curve was adjusted slightly to be consistent with the ZIP+4 sensitivity analyses included in the 1984 USPS proposal to the Postal Board of Governors (savings factors of 1.0, 0.866, and 0.72 at ZIP+4 usage rates of 0.9, 0.76, and 0.57 [corresponds to 90 percent, 76 percent, and 57 percent ZIP+4 usage]).